Water-in-oil emulsion explosives are well-known. For example, such explosive compositions are disclosed in U.S. Pat. Nos. 4,356,044; 4,322,258; 4,141,763; 3,447,978 and 3,161,651. Emulsion explosives are found to have certain advantages over conventional aqueous slurry explosives which have a continuous aqueous phase, as for example described in U.S. Pat. No. 4,141,767. Further explosive compositions are known from Australian patent specifications Nos. 29932/89 (612,787); 67382/89; and 83316/87.
One inherent problem with emulsion explosives however is their relative instability, due to the fact that they include a thermodynamically unstable dispersion of supercooled solution or melt droplets in an oil-continuous phase. If the emulsion remains stable, these supercooled droplets are prevented from crystallising or solidifying into a lower energy state. However, if the emulsion weakens or becomes unstable, then crystallisation or solidification of the droplets results and the explosive composition generally loses some of its sensitivity to detonation and often becomes too viscous to handle for certain blasting operations. Moreover, it is relatively common to add solid components to emulsion explosives, for example in the form of glass microspheres for density reduction and prills or particles of oxidizer salt (such as for example porous prilled ammonium nitrate (AN) for increased energy. These solid components do however in many cases tend to destabilize emulsions.
It is common to use emulsion explosives as a repumpable explosive. That is, as an explosive that is formulated at a facility, and thereafter loaded or pumped into a bulk container and then transported in such a container to a blasting site, where it is repumped form the container into a bore hole. Alternatively, such an explosive may be delivered or repumped into a centrally located storage tank from which it will be further repumped into a vehicle for transportation to a blasting site and the again repumped into a bore hole.
It is therefore important that emulsion explosives remain stable even after being subjected to repeated handling or shearing action which normally tends to destabilise and emulsion. Further the viscosity of such emulsions must remain sufficiently low enough to allow for repumping at reasonable pressures and at a relatively low ambient temperature such as may be experienced during colder months of the year. Repeated handling or shearing action tends to increase an emulsion's viscosity.
It is an object of at least one aspect of the present invention to provide an explosive composition including an emulsifier, which goes some way towards overcoming or minimising the problems associated with explosive compositions known up until this time.
It is a further aspect of at least one aspect of this invention to provide a method of forming an explosive composition.
Other objects of the present invention will become apparent from the following description.